EXECUTIVE SUMMARY

The mangroves constitutea community of usually woody,evergreen, salt tolerant plants of soft and swampy mud of tropical sub-tropical coastal zones preferring river mouths, lagoons and creeks. Mostly found in intertidal zones and stagnant swampy coastal waters they have special adaptations like physiological and structural mechanisms to combat excessive salt in the medium, special aerial root systems for support in unstable slushy substratum and for gaseous exchange as they are anchored in anoxic water-logged conditions.  Some, especially members of Rhizophoraceae have their seeds germinating into seedlings while the fruits are still attached to parent plant. These juvenile seedlings fall vertically into the mud, get stuck there and develop into new plants.

Till about 1960s, mangroves were largely viewed as “economically unproductive areas” and were cut down for meeting a variety of human needs and the swamps reclaimed for human habitations. Mangrove areas today rated among the most productive ecosystems on this planet. They generate nutritionally important detritus for fishes, prawns, crabs, oysters etc. and shelter estuarine and marine organisms and provide safe breeding grounds for many, as well as provide home for numerous kinds of birds.

Mangroves play important role in ecosystem functioning and are of great economic importance for fisheries. Detritus is also transported a food by tides to near-shore organisms.Mangroves contribute to the stabilization of the shoreline and prevention of shore erosion. They serve as a barrier against storms so as to lessen damage to coastal land and residents. The dense network of supporting roots and breathing roots give mechanical support to the tree and trap the sediments. Without mangroves, all silt will be carried into the sea, where turbid water might cause corals to die. Mangrove trees act as sinks, which concentrate pollutants such as sewage, toxic minerals, pesticide, herbicides, etc. They sequester much more carbon per unit area than even tropical rain forests. Wherever mangroves are rich livelihood opportunities for humans are great, including promotion of tourism.

Among the various direct uses of mangrove products are edible fruits and fronds, honey, medicine, timber, fuelwood, manure, tannin, biochemicals, paper-pulp, genes for salt tolerance in crop plants, dyes, bio-fuel for blending with petroleum, fibre, perfume, fish feed etc.

By far tropical Asian countries account for highest area under mangroves. The Sunderbans, along the shores of West Bengal and Bangladesh have the richest and largest mangrove community in the world. Andaman and Nicobar Islands, Orissa, estuaries of Andhra Tamil Nadu and Gujarat have large areas of mangroves.

Mangrove vegetation was neglected totally in Karnataka State and national level surveys hitherto showed no mangroves or only negligible areas under it (just 1 or 2 sq.km), which is far from the reality. As mangroves are inevitable for integrity of estuarine ecosystems and maintaining their high productivity a detailed micro level survey was found to be necessary in every and estuary and creek.
Karnataka estuarine regions are densely populated by humans because of high productivity and transportation facilities that these areas provided in continuity with the Arabian Sea. Bulk of the shallow water coastal swamps areas were presumably cleared for growing salt tolerant rice in reclaimed fields protected from salt water entry by making embankments. Traditionally the farmers planted mangrove trees alongside these bunds. Later when stone bunds were built by the Government, mangroves were cut down in large scale.

The start of Linganmakki dam for power generation in the Sharavathi River would have caused obvious decline in estuarine salinity on account of continuous release of fresh water affecting adversely estuarine ecosystem, particularly mangroves. Such changes went practically unrecorded in science. The arrival of one more dam at Gersoppa in the same river caused still further dilution so much so most of the time estuarine salinity is in near fresh water conditions. The mangrove diversity declined as a consequence leaving behind very few species, especially the tree Sonneratiacaseolaris, tolerant of nearly fresh water conditions.

Recent decades witnessed spurt of shrimp farming activities in specially prepared shrimp ponds from which every trace of mangroves were removed.

At present there is increased awareness on the importance of mangroves. Under various schemes sponsored by State and Central Governments mangrove plantings have been made in the estuaries of Karnataka. TheHonavarForest Division achieved spectacular progress in mangrove afforestation, especially in Aghanashini estuary and Kumta creek. Increased area under mangroves is bound to have beneficial effects on estuarine productivity and biodiversity as well as causing increased nutrient flow into the Arabian Sea itself.

In spite of such progress, in the absence of overall evaluation and mapping of the mangrove situation it has become difficult to take up the cause for further afforestation of Karnataka’s estuaries with mangroves. As evaluation requires mapping of existing mangroves and depiction of suitable areas for further planting a detailed estuary and creek-wise surveyis found necessary. Moreover estuaries need to be demarcated into different salinity zones for making appropriate combination of species for planting in high, medium and low salinity zones. The current study was carried out at the behest of Honavar Forest Division of Kanara Forest Circle.

Of the methods used for the survey were all out field studies, physically visiting all the estuaries and creeks and noting down mangrove species present in different patches through sampling, and finding out the geo-locations by using GPS. Google imageries have been very useful in locating mangrove patches and in estimating the potential intertidal areas for future planting. Counts of trees were made in selected locations to find out percentage composition of species. Salinity levels were noted down to classify mangroves into high, medium and low salinity species. Remote sensing imageries had only limited applications for identifying mangrove trees on the substratum, but nevertheless estimates were done of the area under frequently occurring tree mangroves. RS data of 1989, 2000, 2003 and 2010 helped in finding out changes in land use land cover in the estuaries, including one km buffer zone outside.

Honavar Division has four estuaries towards the river mouths of Aghanashini, Sharavathi, Venktapur and part of Gangavali. The Badgani River merges with the Sharavathi estuary towards its mouth. All the estuaries have normal rise and fall of  marine tides and normal ranges of salinity expected of local estuaries except the Sharavathi estuary which has minimal salinity (<0.5 ppt) most of the time due to constant release of fresh water from hydro-electric projects from upstream areas. This has caused major decline in mangrove diversity as high salinity mangroves have totally vanished and medium salinity ones turned minimal and low salinity ones, mainly Sonneratiacaseolarisfavoured.

A detailed distribution map of Honavar Forest Division will be help in assessing range-wise, section-wise and beat-wise and estuary and creek-wise mapping of mangroves. This is expected to facilitate more efficient management of mangroves. The mapping also covered mangrove associates. The true mangroves (confined to estuaries and creeks)of Honavar Division belong to 6 families, 8 genera and 11 species.  If we exclude the exclusive estuarine grass Porteresiacoarctatathe species number will decline to 10. In addition, a fern, Acrostichumaureumalso occurs in mangrove habitats of less brackish habitats. Rhizophoraceae members Rhizophoramucronata, R. apiculata, Kandeliakandel and Bruguieragymnorrhizaare typicalmangroves with stilt roots and viviparous seeds. Bruguiera occurs nowhere except sparingly in Venktapur estuary.

The study covered also about 32 species of notable mangrove associate species which have also distribution beyond the mangrove areas in the lands away from estuaries.

Mangroves of the estuaries and creeks are in high state of fragmentation due to high degree of human impacts through centuries, which include reclamation of estuaries for rice and coconut cultivation, expansion of human settlements, shrimp farming, salt production, shell and sand mining, cutting for fuel and minor timber etc. Altogether 1549 patches were recognized in the Forest Division. These also include linear patches along the borders of estuaries.

We have estimated 391 ha of mangrove areas and 1019 ha suitable for planting. If we consider rangewise mangrove area highest (128 ha) is in Honavar Range, followed by Hiregutti Range (88 ha) and the least occurs in Manki Range (4 ha). Manki also does not have any area for mangrove planting. Hiregutti Range also has largest area (708 ha) suitable for mangrove planting.Honavar Range has 161 ha for mangrove planting while Kumta has 91 ha. In Chapter 3 (section 3.1) is provided all the details regarding administrative unitwise (range, section and beat) area under mangroves and suitable areas for planting.

In Chapter 3 (section 3.2) estuary-wise and creekwise mangrove area and potential area for planting are given. Area under mangroves is highest (169 ha) in Aghanashini estuary, followed by Sharavathi-Badgani (136 ha) and Gangavali (46 ha). Considering estuary-wise suitable area for mangrove planting Aghanashini has highest (711 ha), followed by Sharavathi-Badgani (184 ha), Gangavali (95 ha) and Kumta creek (42 ha). Even the smallest creeks of less than 1 ha are considered in this study.

Whereas Rhizophoraapiculataand Avicenniamarina  are high salinity mangroves (>15 ppt.), Aegicerascorniculatumprefers medium salinity zones (5-15 ppt). Rhizophoramucronata, Avicenniaofficinalis, Sonneratiaalba, Kandeliakandeland Excoecariaagallochaare seen in high and medium salinity zones. Acanthus ilicifoliusoccurs in all salinity zones, but Sonneratiacaseolaris has presence in medium to very low salinity (< 0.5 ppt) conditions.Estuarywise and villagewise details of mangrove species present are given in Chapter 3 (section 3.2).

During mangrove afforestation in the estuaries care should be taken to avoid planting in bivalve and oyster beds which are highly productive of food for humans and animals, including several species of birds.

Rangewise and beat wise mangrove areas and potential areas for planting are shown in maps for the convenience of forest department staff involved in mangrove protection and planting (Chapter 3, Section 3.3). The annexures contain very detailed information on sectionwise and beat area under mangroves and suitable areas for planting.

RECOMMENDATIONS

The exercise carried out in minute details could be of great help to the Forest Department in mangrove management. Mangroves are classified under CRZ-I area and therefore mangrove maps could be used for delineating CRZ I areas.

• It is recommended that similar exercises be carried out in other estuaries of Karnataka as well, considering the tremendous ecological and economic uses of mangroves

• As Rhizophoramucronatais the main species used for mangrove afforestation, such monoculturing has to be avoided in future giving way to fair mixing of other species. More importance should be given to Avicenniaspp. and Sonneratiaspp.

• The rare population of Bruguieragymnorrhizain Venktapur estuary should be protected and more number of seedlings should be introduced here from Kali or Kundapur estuaries, as local regeneration is poor.

• Many aquaculture ponds are abandoned due to losses suffered by shrimp farmers. They are also unfit for rice cultivation. Government may formulate a scheme to acquire such areas for planting with mangroves.

• Honey production in mangrove areas is a totally neglected economic activity in Honavar Division as well as in the entire coastal Karnataka. As mangrove honey with rare mix of salts can have greater value bee keeping experiments should be carried out in the estuarine areas.

• Mangrove based tourism for bird watching and for scenic enjoyment should be promoted as a good income generating activity for the local VFCs (Village Forest Committees). Appropriate training for local youth in arranging such mangrove tours will provide newer livelihood opportunites.